1. Field of the Invention
The present invention relates to a wrench with a fixed maximum operational torque to prevent damage to the object secured by a fastener driven by the wrench.
2. Description of the Related Art
FIG. 12A of the drawings illustrates a conventional wrench 1 having a hexagonal driving portion with six planar faces 2 for engaging with six faces of a hexagonal groove in a top face of a fastener. However, slide tends to occur between the planar faces of the driving portion of the wrench 1 and the faces of the fastener. FIG. 12B illustrates a so-called TROX wrench 3 having plural arcuate faces 4 for engaging with corresponding arcuate faces in a top face of a fastener. Such a TROX wrench 3 is used to tighten important parts of a car and cutting tools. As illustrated in FIG. 13, a blade 7 is tightened to a cutting tool 5 by a bolt 6. However, the expensive blade 7 tends to be damaged when the bolt 6 is excessively tightened. But the blade 7 could fly away and thus cause injury if the bolt 6 is not tightened to the desired extent.
An object of the present invention is to provide a wrench with a fixed maximum operational torque such that when the torque applied by the user is greater than the maximum operational torque, the wrench slides and the fastener is not turned. Thus, damage to the object secured by the fastener is prevented.
Another object of the present invention is to provide a wrench with a fixed maximum operational torque that can be altered in response to the actual use.
A wrench in accordance with the present invention comprises a rod, a slide control member, a casing for rotatably accommodating the slide control member, and a retaining means. The rod comprises a driving portion on an end thereof for engaging with a fastener. The slide control member is securely mounted to the rod to turn therewith. The retaining means is mounted in the casing and includes an end operably connected to the slide control member. When a rotational force applied to the casing is smaller than an engaging force between the slide control member and the end of the retaining means, the slide control member and the rod are turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force between the slide control member and the end of the retaining means, the casing slides while the slide control member and the rod are not turned.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.